Object Relational Mapping(ORM)

Persistence

• Almost all applications require some form of persistence.• Almost all persistence is done using relational

databases.• Usually the business classes are the ones that are

persisted.

Actual ExamplelsSqlStatement = "INSERT INTO tblClaimsHistory " +

"(fldBatchLet, fldBatchNum, fldBatchFy,fldBatchReqSeq, fldPatientSSN,fldProvTaxId,fldProvSuff,fldProvType,"+

"fldDiag1,fldDiag2,fldDiag3,fldDiag4, " + "fldPatientLastName, fldPatientFirstName, fldProviderName ," +

"fldTotalCharged,fldTotalToPay,fldTotalDue,fldTotalCalcAmount,fldTotalPaid, "+"fldRecDate, fldClaimBeginDate,

fldClaimEndDate,fldCurrDocNum, fldMailCode, MessageIdentifier ) " + "VALUES ('"+lsBatchNum.Substring(0,1)+"',"+lsBatchNum.Substring(1)+","+lsBatchFy+",'"+ lsBatchReqSeq + "', '" +lsSSN+"','"+lsFedTaxID+"','"+lsProvTaxSfx+"','"+ lsProviderType +"','"+ fldDiag1+"','"+fldDiag2+"','"+fldDiag3+"','"+fldDiag4 +fldPatientLastName+"','"+fldPatientFirstName+"','" +lsProviderName+"',"+

fldTotalCharged+","+fldTotalToPay+","+fldTotalDue+","+fldTotalCalcAmount+","+fldTotalAmtPaid +",'"+ ClaimRecievedDate + "','" + fldClaimBeginDate + "','" + fldClaimEndDate + "','"+fldCurrDocNum+"','"+fldMailCode+"','"+MessageIdentifier+"') " +"SELECT @@IDENTITY AS 'Identity'";

And as preparation we need:

lsBeginDate = lsBeginDate.Replace("-", "/");

lsEndDate = lsEndDate.Replace("-", "/");

OR

Replace("'","''");

Usually we have

• A business Object • & A database Table

-ID-Name-Description-Address

CustomerCustomer

ID Name Desciption Addresss

Traditional way to handle persistence

• Using a N-Tier design– UI Tier– Business Tier– Data Tier– Database

UI tier

Data Tier

Business tier

Dat

aba

se

This approach requires

• Long and tedious work to:– Build SQL statements for Insert, update, Delete,

select– Send the Objects’ properties to the data layer as

parameters– Account for different types of databases/data fields

(ex: ‘ ‘ for strings and dates, format dates, handling Null values,..

– Handle IDs, Keys,..

This work is usually..

• Time Consuming• Boring• Error Prone• And most importantly:

– Doesn’t require much thinking– Shifts focus from main target ( handle business case)

ORM

• ORM is about Mapping an Object to one or more database tables.

• It eliminates the need to create a data layer tier ( data layer is implicit)

• “In a nutshell, object/relational mapping is the automated (and transparent) persistence of objects in an application to the tables in a relational database, using metadata that describes the mapping between the objects and the database.”

• In short: ORM saves you from writing boring and error prone code thus saving time and getting better quality.

Main Advantages of ORM

• Better productivity ( no more tedious coding)• Better performance• DB independence• Less error prone

Many ORM tools, Many Approaches

• There are different Tools for implementing ORM using different approach– Using Attributes in the classes (GENTLE.NET)– Using XML mapping Files (NHIBERNATE)– Using Visual Mapping,– … etc.

Introduction to GENTLE.NET

• Open source, free tool.• Supports many DB types.• Uses attributes .. No complex configuration files• Queries generated at runtime using features in the .NET

framework (class attributes)• Handles “impedance mismatch” (Null values, auto

generated keys,..)• Handles transactions• Supports caching• Supports validations on the object level

Example Classpublic class User{

private int userId;private string userName;public User( int userId, string userName

){

this.userId = userId;this.userName = userName;

}public int Id{

get{ return userId; }set{ userId = value; }

}public string Name{

get{ return userName; }set{ userName = value; }

}}

• To be saved in

User

ID Name

All we need to do is

1. Add reference to 3 DLLs

2. Add 3 “using..” lines

3. Add appropriate attributes to object propertied

Class Becomesusing Gentle.Framework;[TableName("Users")]public class User : Persistent{

private int userId;private string userName;// this is used by clients to construct new userspublic User( string userName ) : this( 0, userName ) {}// this is used by Gentle to reconstruct objects read from the databasepublic User( int userId, string userName ){

this.userId = userId;this.userName = userName;

}// this is used by client to fetch users from the databasestatic public User Retrieve( int userId ){

Key key = new Key( typeof(User), true, "Id", userId );return Broker.RetrieveInstance( typeof(User), key ) as User;

}[TableColumn("UserId"), PrimaryKey(AutoGenerated=true)]public int Id{

get{ return userId; }set{ userId = value; }

}[TableColumn(NotNull=true)]public string Name{

get{ return userName; }set{ userName = value; }

}}

• That was all the “SQL” we need to write.• Also we don’t need to “create” an object

from a row in DB. It is done implicitly• To save an object all we need to do is:

User ford = new User( "Ford Prefect" );ford.Persist();

• To Load an object all we need to do is:User prefect = User.Retrieve( ford.Id );Using Id ( or any other Key)

BINGO !!!

Demo

AdditivesUsing SQL builder

static public IList ListByNameStartsWith( string partialName ){SqlBuilder sb = new SqlBuilder( StatementType.Select, typeof(User) );// note: the partialName parameter must also contain the %'s for the LIKE query!

sb.AddConstraint( Operator.Like, "Name", partialName );// passing true indicates that we'd like a list of elements, i.e. that no primary key// constraints from the type being retrieved should be added to the statement

SqlStatement stmt = sb.GetStatement( true );// execute the statement/query and create a collection of User instances from the

result setreturn ObjectFactory.GetCollection( typeof(User), stmt.Execute() );}

Additives

• Retrieving Lists of objects

• IList is directly bindable with data grids.

GentleList list = new GentleList( typeof(User), parentInstance );

Additives

• Generating business class using MyGeneration– Demo

References

• http://www.mertner.com/projects/gentle

• http://www.mygenerationsoftware.com

Thank You!

Emad Magdy